1. Field of the Invention
The invention deals in general terms with the field of radio-frequency circuits, and in particular the invention relates to a glass material which is suitable for the production of conductor structures appropriate for radio-frequency applications on a substrate, and also to a radio-frequency substrate.
2. Description of Related Art
It is known that the trend in the semiconductor industry is toward ever higher data transmission rates. Frequencies in the gigahertz range lead to increased signal attenuation at the feed and emission systems. Hitherto, primarily printed ceramic (HTCC) and glass-ceramic (LTCC) multiple layers, which after they have been printed with conductive layers, laminated and sintered, realize a three-dimensional or multilayer wiring for a radio-frequency circuit, have been used for systems of this type. Moreover, organic multiple layers which are not hermetic are also used. However, at high frequencies, the transmission losses in wiring systems of this type increase on account of the attenuation in the interconnects. The use of HTCC and LTCC materials at very high frequencies—generally over 40 GHz—is restricted by the relatively high dielectric constants (DK) and loss angles (tan δ) in these frequency ranges. The HTCC and LTCC ceramics have an inevitable granularity which has an adverse effect on the radio-frequency properties and leads to the interconnects integrated therein having a surface roughness corresponding to the granularity. This surface roughness leads to increased line losses.
A further cause of the high degree of attenuation in known radio-frequency conductor substrates resides, inter alia, in the application of the interconnects, usually by means of thick-film technology, in particular by means of screen printing. The interconnects produced using this technology have a considerable inhomogeneity and roughness of the interconnect contours. The inhomogeneities of the interconnects act as antennas, leading to extensive losses through radiation.
Furthermore, sintering inevitably leads to shrinkage of the substrates, which makes it difficult to accurately maintain desired dimensions.
More recent developments have been toward replacing the disadvantageous thick-film technology by using various PVD processes to apply the interconnects by evaporation coating or sputtering. However, the sintering of the HTCC or LTCC materials to produce the wiring stack required in previous processors still presents a major problem. For example, sintering of an LTCC ceramic requires a temperature of at least 950° C. A temperature of 1500° C. is required for the sintering of HTCC ceramics. These temperatures lead to changes in the interconnect structures, and the choice of interconnect materials is limited.